Bolometric detectors, also named as bolometers, are thermal infrared sensors that absorb electromagnetic radiation, which causes an increase in temperature. The resulting temperature increase is a function of the radiant energy striking the bolometer and may be measured with thermoelectric, pyroelectric, resistive components. Accordingly, bolometers are able to detect or measure electromagnetic radiation.
FIG. 1A shows a conventional bolometer 100a employing a sensing resistor 102. FIG. 1A shows an infrared (IR) absorbing layer 104, the sensing resistor 102 in thermal connection with layer 104, a thermostat 106, and a link 108 connecting the sensing resistor 102 with the thermostat.
FIG. 1B shows another conventional bolometer 100b, which relies on changes in resistance to measure electromagnetic radiation. FIG. 1B shows an absorber layer 110 for absorbing infrared (IR) radiation, a sensitive layer 112 for sensing the IR radiation, a gold (Au) layer 114 for reflecting IR radiation towards layer 112, and a silicon nitride layer 116 for encapsulating the sensitive layer 112.
The change in resistance, ΔR, is provided by
                    Δ        ⁢                                  ⁢        R                    R        0              =          α      ⁢                          ⁢      Δ      ⁢                          ⁢      T        ,where R0 is the initial resistance, ΔT is the change in temperature, and α is the temperature coefficient of resistance. The change in temperature may be provided by
            Δ      ⁢                          ⁢      T        =                  η        ⁢                                  ⁢                  P          0                                      G          th                ⁢                              1            +                          4              ⁢                                                          ⁢                              π                2                            ⁢                              f                2                            ⁢                              τ                2                                                          ,where P0 is the power of the input light received, η is the absorption coefficient of the bolometer, Gth is the thermal conductance between the bolometer and surrounding thermal environment, f is the modulation frequency of the input light, and τ is the time constant of the bolometer. The time constant of the bolometer may be provided by
      τ    =                  C        th                    G        th              ,where Cth is the thermal capacity of the bolometer, and Gth is the thermal conductance between the bolometer and surrounding thermal environment as provided earlier.
The bolometers are used in a wide variety of applications, such as in non-dispersive infrared (NDIR) gas sensing, thermography, firefighting, and security. However, most of current bolometric transducers are designed for free-space optics applications, which may result in low efficiency, and high power consumption. Also, their sensitivities may be limited by the low temperature coefficient of resistance (α), as well as low conversion of radiant energy to heat energy. Additionally, conventional bolometers may also suffer from response speed, which is often in the range of milliseconds (ms).